Eyepiece for virtual, augmented, or mixed reality systems

ABSTRACT

An eyepiece waveguide for an augmented reality. The eyepiece waveguide can include a transparent substrate with an input coupler region, a first orthogonal pupil expander (OPE) region, and an exit pupil expander (EPE) region. The input coupler region can couple an input light beam that is externally incident on the input coupler region into at least a first guided light beam that propagates inside the substrate. The first OPE region can divide the first guided beam into a plurality of replicated, spaced-apart beams. The EPE region can re-direct the replicated beams from the first OPE region such that they exit the substrate. The EPE region can have an amount of optical power.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/877,117, filed Jan. 22, 2018, and entitled “EYEPIECE FOR VIRTUAL,AUGMENTED, OR MIXED REALITY SYSTEMS,” which claims priority to U.S.Patent Application No. 62/449,524, filed Jan. 23, 2017, and entitled“EYEPIECE FOR VIRTUAL, AUGMENTED, OR MIXED REALITY SYSTEMS.” Theforegoing applications and any others for which a foreign or domesticpriority claim is identified in the Application Data Sheet as filed withthe present application are hereby incorporated by reference under 37CFR 1.57.

BACKGROUND Field

This disclosure relates to eyepieces for virtual reality, augmentedreality, and mixed reality systems.

Description of the Related Art

Modern computing and display technologies have facilitated thedevelopment of virtual reality, augmented reality, and mixed realitysystems. Virtual reality, or “VR,” systems create a simulatedenvironment for a user to experience. This can be done by presentingcomputer-generated image data to the user through a head-mounteddisplay. This image data creates a sensory experience which immerses theuser in the simulated environment. A virtual reality scenario typicallyinvolves presentation of only computer-generated image data rather thanalso including actual real-world image data.

Augmented reality systems generally supplement a real-world environmentwith simulated elements. For example, augmented reality, or “AR,”systems may provide a user with a view of the surrounding real-worldenvironment via a head-mounted display. However, computer-generatedimage data can also be presented on the display to enhance thereal-world environment. This computer-generated image data can includeelements which are contextually-related to the real-world environment.Such elements can include simulated text, images, objects, etc. Mixedreality, or “MR,” systems are a type of AR system which also introducesimulated objects into a real-world environment, but these objectstypically feature a greater degree of interactivity. The simulatedelements can often times be interactive in real time.

FIG. 1 depicts an example AR/MR scene 1 where a user sees a real-worldpark setting 6 featuring people, trees, buildings in the background, anda concrete platform 20. In addition to these items, computer-generatedimage data is also presented to the user. The computer-generated imagedata can include, for example, a robot statue 10 standing upon thereal-world platform 20, and a cartoon-like avatar character 2 flying bywhich seems to be a personification of a bumble bee, even though theseelements 2, 10 are not actually present in the real-world environment.

SUMMARY

An eyepiece for a virtual reality, augmented reality, or mixed realitysystem is disclosed. In some embodiments, the eyepiece comprises: afirst waveguide substrate that is at least partially transparent; aninput coupler region formed on or in the first waveguide substrate andconfigured to couple at least one input light beam that is externallyincident on the input coupler region into at least a first guided lightbeam that propagates inside the first waveguide substrate; a firstorthogonal pupil expander (OPE) region formed on or in the firstwaveguide substrate and configured to divide the first guided light beamfrom the input coupler region into a plurality of parallel, spaced-apartlight beams; and an exit pupil expander (EPE) region formed on or in thefirst waveguide substrate and configured to re-direct the light beamsfrom the first OPE region such that they exit the first waveguidesubstrate, the EPE region comprising an amount of optical power.

In some embodiments, the EPE region comprises a diffraction grating tore-direct the light beams from the first OPE region such that they exitthe first waveguide substrate, and wherein the diffraction grating ofthe EPE region comprises a plurality of curved lines whose curvaturedetermines the optical power of the EPE region.

In some embodiments, the first waveguide substrate is configured tooutput a plurality of output beams such that they correspond to a firstdepth plane, the first depth plane being determined by the optical powerof the EPE region of the first waveguide substrate.

In some embodiments, the eyepiece further comprises: a second waveguidesubstrate with an input coupler region, a first OPE region, and an EPEregion, wherein the EPE region of the second waveguide substratecomprises an amount of optical power that is different than the opticalpower of the EPE region of the first waveguide substrate, and whereinthe second waveguide substrate is configured to output a plurality ofoutput beams such that they correspond to a second depth plane that isdifferent from the first depth plane, the second depth plane beingdetermined by the optical power of the EPE region of the secondwaveguide substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a user's view of an augmented reality (AR) scenethrough an AR system.

FIG. 2 illustrates an example of a wearable display system.

FIG. 3 illustrates a conventional display system for simulatingthree-dimensional image data for a user.

FIG. 4 illustrates aspects of an approach for simulatingthree-dimensional image data using multiple depth planes.

FIGS. 5A-5C illustrate relationships between radius of curvature andfocal radius.

FIG. 6 illustrates an example of a waveguide stack for outputting imageinformation to a user in an AR eyepiece.

FIGS. 7A-7B illustrate examples of exit beams outputted by a waveguide.

FIG. 8 illustrates an example of a stacked waveguide assembly in whicheach depth plane includes images formed using multiple differentcomponent colors.

FIG. 9A illustrates a cross-sectional side view of an example of a setof stacked waveguides that each includes an in-coupling optical element.

FIG. 9B illustrates a perspective view of an example of the plurality ofstacked waveguides of FIG. 9A.

FIG. 9C illustrates a top-down plan view of an example of the pluralityof stacked waveguides of FIGS. 9A and 9B.

FIG. 10 is a perspective view of an example AR eyepiece waveguide stack.

FIG. 11 is a cross-sectional view of a portion of an example eyepiecewaveguide stack with an edge seal structure for supporting eyepiecewaveguides in a stacked configuration.

FIGS. 12A and 12B illustrate top views of an eyepiece waveguide inoperation as it projects an image toward a user's eye.

FIG. 13A illustrates a front view (in the as-worn position) of one halfof an example eyepiece for a VR/AR/MR system.

FIG. 13B illustrates some of the diffractive optical features of aneyepiece which cause image data projected into the eyepiece at an inputcoupler region to propagate through the eyepiece and to be projected outtoward the user's eye from an exit pupil expander (EPE) region.

FIG. 13C illustrates the optical operation of the orthogonal pupilexpander (OPE) regions shown in FIG. 9B.

FIG. 14A illustrates an embodiment of an eyepiece which includes aninput coupler region having a crossed diffraction grating.

FIG. 14B is a perspective view of an example embodiment of the inputcoupler region shown in FIG. 14A made up of a crossed diffractiongrating.

FIG. 15A illustrates an embodiment of an eyepiece with upper and lowerOPE regions which are angled toward an EPE region to provide a morecompact form factor.

FIG. 15B illustrates an example embodiment of the diffractive opticalfeatures of the input coupler region of the eyepiece shown in FIG. 15A.

FIG. 15C illustrates an example embodiment of the diffractive opticalfeatures of the OPE region of the eyepiece shown in FIG. 15A.

DETAILED DESCRIPTION

Example HMD Device

Virtual and augmented reality systems disclosed herein can include adisplay which presents computer-generated image data to a user. In someembodiments, the display systems are wearable, which may advantageouslyprovide a more immersive VR or AR experience. FIG. 2 illustrates anexample wearable display system 60. The display system 60 includes adisplay or eyepiece 70, and various mechanical and electronic modulesand systems to support the functioning of that display 70. The display70 may be coupled to a frame 80, which is wearable by a display systemuser 90 and which is configured to position the display 70 in front ofthe eyes of the user 90. The display 70 may be considered eyewear insome embodiments. In some embodiments, a speaker 100 is coupled to theframe 80 and is positioned adjacent the ear canal of the user 90. Thedisplay system may also include one or more microphones 110 to detectsound. The microphone 110 can allow the user to provide inputs orcommands to the system 60 (e.g., the selection of voice menu commands,natural language questions, etc.), and/or can allow audio communicationwith other persons (e.g., with other users of similar display systems).The microphone 110 can also collect audio data from the user'ssurroundings (e.g., sounds from the user and/or environment). In someembodiments, the display system may also include a peripheral sensor 120a, which may be separate from the frame 80 and attached to the body ofthe user 90 (e.g., on the head, torso, an extremity, etc.). Theperipheral sensor 120 a may acquire data characterizing thephysiological state of the user 90 in some embodiments.

The display 70 is operatively coupled by a communications link 130, suchas by a wired lead or wireless connectivity, to a local data processingmodule 140 which may be mounted in a variety of configurations, such asfixedly attached to the frame 80, fixedly attached to a helmet or hatworn by the user, embedded in headphones, or removably attached to theuser 90 (e.g., in a backpack-style configuration or in a belt-couplingstyle configuration). Similarly, the sensor 120 a may be operativelycoupled by communications link 120 b (e.g., a wired lead or wirelessconnectivity) to the local processor and data module 140. The localprocessing and data module 140 may include a hardware processor, as wellas digital memory, such as non-volatile memory (e.g., flash memory or ahard disk drive), both of which may be utilized to assist in theprocessing, caching, and storage of data. The data may include data 1)captured from sensors (which may be, e.g., operatively coupled to theframe 80 or otherwise attached to the user 90), such as image capturedevices (e.g., cameras), microphones, inertial measurement units,accelerometers, compasses, GPS units, radio devices, gyros, and/or othersensors disclosed herein; and/or 2) acquired and/or processed using aremote processing module 150 and/or a remote data repository 160(including data relating to virtual content), possibly for passage tothe display 70 after such processing or retrieval. The local processingand data module 140 may be operatively coupled by communication links170, 180, such as via a wired or wireless communication links, to theremote processing module 150 and the remote data repository 160 suchthat these remote modules 150, 160 are operatively coupled to each otherand available as resources to the local processing and data module 140.In some embodiments, the local processing and data module 140 mayinclude one or more of the image capture devices, microphones, inertialmeasurement units, accelerometers, compasses, GPS units, radio devices,and/or gyros. In some other embodiments, one or more of these sensorsmay be attached to the frame 80, or may be standalone devices thatcommunicate with the local processing and data module 140 by wired orwireless communication pathways.

The remote processing module 150 may include one or more processors toanalyze and process data, such as image and audio information. In someembodiments, the remote data repository 160 may be a digital datastorage facility, which may be available through the internet or othernetworking configuration in a “cloud” resource configuration. In someembodiments, the remote data repository 160 may include one or moreremote servers, which provide information (e.g., information forgenerating augmented reality content) to the local processing and datamodule 140 and/or the remote processing module 150. In otherembodiments, all data is stored and all computations are performed inthe local processing and data module, allowing fully autonomous use froma remote module.

The perception of an image as being “three-dimensional” or “3-D” may beachieved by providing slightly different presentations of the image toeach eye of the user. FIG. 3 illustrates a conventional display systemfor simulating three-dimensional image data for a user. Two distinctimages 190, 200—one for each eye 210, 220—are output to the user. Theimages 190, 200 are spaced from the eyes 210, 220 by a distance 230along an optical or z-axis that is parallel to the line of sight of theuser. The images 190, 200 are flat and the eyes 210, 220 may focus onthe images by assuming a single accommodated state. Such 3-D displaysystems rely on the human visual system to combine the images 190, 200to provide a perception of depth and/or scale for the combined image.

However, the human visual system is complicated and providing arealistic perception of depth is challenging. For example, many users ofconventional “3-D” display systems find such systems to be uncomfortableor may not perceive a sense of depth at all. Objects may be perceived asbeing “three-dimensional” due to a combination of vergence andaccommodation. Vergence movements (e.g., rotation of the eyes so thatthe pupils move toward or away from each other to converge therespective lines of sight of the eyes to fixate upon an object) of thetwo eyes relative to each other are closely associated with focusing (or“accommodation”) of the lenses of the eyes. Under normal conditions,changing the focus of the lenses of the eyes, or accommodating the eyes,to change focus from one object to another object at a differentdistance will automatically cause a matching change in vergence to thesame distance, under a relationship known as the “accommodation-vergencereflex,” as well as pupil dilation or constriction. Likewise, undernormal conditions, a change in vergence will trigger a matching changein accommodation of lens shape and pupil size. As noted herein, manystereoscopic or “3-D” display systems display a scene using slightlydifferent presentations (and, so, slightly different images) to each eyesuch that a three-dimensional perspective is perceived by the humanvisual system. Such systems can be uncomfortable for some users,however, since they simply provide image information at a singleaccommodated state and work against the “accommodation-vergence reflex.”Display systems that provide a better match between accommodation andvergence may form more realistic and comfortable simulations ofthree-dimensional image data.

FIG. 4 illustrates aspects of an approach for simulatingthree-dimensional image data using multiple depth planes. With referenceto FIG. 4, the eyes 210, 220 assume different accommodated states tofocus on objects at various distances on the z-axis. Consequently, aparticular accommodated state may be said to be associated with aparticular one of the illustrated depth planes 240, which has anassociated focal distance, such that objects or parts of objects in aparticular depth plane are in focus when the eye is in the accommodatedstate for that depth plane. In some embodiments, three-dimensional imagedata may be simulated by providing different presentations of an imagefor each of the eyes 210, 220, and also by providing differentpresentations of the image corresponding to multiple depth planes. Whilethe respective fields of view of the eyes 210, 220 are shown as beingseparate for clarity of illustration, they may overlap, for example, asdistance along the z-axis increases. In addition, while the depth planesare shown as being flat for ease of illustration, it will be appreciatedthat the contours of a depth plane may be curved in physical space, suchthat all features in a depth plane are in focus with the eye in aparticular accommodated state.

The distance between an object and an eye 210 or 220 may also change theamount of divergence of light from that object, as viewed by that eye.FIGS. 5A-5C illustrate relationships between distance and the divergenceof light rays. The distance between the object and the eye 210 isrepresented by, in order of decreasing distance, R1, R2, and R3. Asshown in FIGS. 5A-5C, the light rays become more divergent as distanceto the object decreases. As distance increases, the light rays becomemore collimated. Stated another way, it may be said that the light fieldproduced by a point (the object or a part of the object) has a sphericalwavefront curvature, which is a function of how far away the point isfrom the eye of the user. The curvature increases with decreasingdistance between the object and the eye 210. Consequently, at differentdepth planes, the degree of divergence of light rays is also different,with the degree of divergence increasing with decreasing distancebetween depth planes and the user's eye 210. While only a single eye 210is illustrated for clarity of illustration in FIGS. 5A-5C and otherfigures herein, it will be appreciated that the discussions regardingthe eye 210 may be applied to both eyes 210 and 220 of a user.

A highly believable simulation of perceived depth may be achieved byproviding, to the eye, different presentations of an image correspondingto each of a limited number of depth planes. The different presentationsmay be separately focused by the user's eye, thereby helping to providethe user with depth cues based on the amount of accommodation of the eyerequired to bring into focus different image features for the scenelocated on different depth planes and/or based on observing differentimage features on different depth planes being out of focus.

Example of a Waveguide Stack Assembly for an AR or MR Eyepiece

FIG. 6 illustrates an example of a waveguide stack for outputting imageinformation to a user in an AR eyepiece. A display system 250 includes astack of waveguides, or stacked waveguide assembly, 260 that may beutilized to provide three-dimensional perception to the eye/brain usinga plurality of waveguides 270, 280, 290, 300, 310. In some embodiments,the display system 250 is the system 60 of FIG. 2, with FIG. 6schematically showing some parts of that system 60 in greater detail.For example, the waveguide assembly 260 may be part of the display 70 ofFIG. 2. It will be appreciated that the display system 250 may beconsidered a light field display in some embodiments.

The waveguide assembly 260 may also include a plurality of features 320,330, 340, 350 between the waveguides. In some embodiments, the features320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280,290, 300, 310 and/or the plurality of lenses 320, 330, 340, 350 may beconfigured to send image information to the eye with various levels ofwavefront curvature or light ray divergence. Each waveguide level may beassociated with a particular depth plane and may be configured to outputimage information corresponding to that depth plane. Image injectiondevices 360, 370, 380, 390, 400 may function as a source of light forthe waveguides and may be utilized to inject image information into thewaveguides 270, 280, 290, 300, 310, each of which may be configured, asdescribed herein, to distribute incoming light across each respectivewaveguide, for output toward the eye 210. Light exits an output surface410, 420, 430, 440, 450 of each respective image injection device 360,370, 380, 390, 400 and is injected into a corresponding input surface460, 470, 480, 490, 500 of the respective waveguides 270, 280, 290, 300,310. In some embodiments, the each of the input surfaces 460, 470, 480,490, 500 may be an edge of a corresponding waveguide, or may be part ofa major surface of the corresponding waveguide (that is, one of thewaveguide surfaces directly facing the world 510 or the user's eye 210).In some embodiments, a beam of light (e.g. a collimated beam) may beinjected into each waveguide and may be replicated, such as by samplinginto beamlets by diffraction, in the waveguide and then directed towardthe eye 210 with an amount of optical power corresponding to the depthplane associated with that particular waveguide. In some embodiments, asingle one of the image injection devices 360, 370, 380, 390, 400 may beassociated with, and inject light into, a plurality (e.g., three) of thewaveguides 270, 280, 290, 300, 310.

In some embodiments, the image injection devices 360, 370, 380, 390, 400are discrete displays that each produce image information for injectioninto a corresponding waveguide 270, 280, 290, 300, 310, respectively. Insome other embodiments, the image injection devices 360, 370, 380, 390,400 are the output ends of a single multiplexed display which maytransmit image information via one or more optical conduits (such asfiber optic cables) to each of the image injection devices 360, 370,380, 390, 400. It will be appreciated that the image informationprovided by the image injection devices 360, 370, 380, 390, 400 mayinclude light of different wavelengths, or colors.

In some embodiments, the light injected into the waveguides 270, 280,290, 300, 310 is provided by a light projector system 520, whichincludes a light module 530, which may include a light source or lightemitter, such as a light emitting diode (LED). The light from the lightmodule 530 may be directed to, and modulated by, a light modulator 540(e.g., a spatial light modulator), via a beamsplitter (BS) 550. Thelight modulator 540 may spatially and/or temporally change the perceivedintensity of the light injected into the waveguides 270, 280, 290, 300,310. Examples of spatial light modulators include liquid crystaldisplays (LCD), including a liquid crystal on silicon (LCOS) displays,and digital light processing (DLP) displays.

In some embodiments, the light projector system 520, or one or morecomponents thereof, may be attached to the frame 80 (FIG. 2). Forexample, the light projector system 520 may be part of a temporalportion (e.g., ear stem 82) of the frame 80 or disposed at an edge ofthe display 70. In some embodiments, the light module 530 may beseparate from the BS 550 and/or light modulator 540.

In some embodiments, the display system 250 may be a scanning fiberdisplay comprising one or more scanning fibers to project light invarious patterns (e.g., raster scan, spiral scan, Lissajous patterns,etc.) into one or more waveguides 270, 280, 290, 300, 310 and ultimatelyinto the eye 210 of the user. In some embodiments, the illustrated imageinjection devices 360, 370, 380, 390, 400 may schematically represent asingle scanning fiber or a bundle of scanning fibers configured toinject light into one or a plurality of the waveguides 270, 280, 290,300, 310. In some other embodiments, the illustrated image injectiondevices 360, 370, 380, 390, 400 may schematically represent a pluralityof scanning fibers or a plurality of bundles of scanning fibers, each ofwhich are configured to inject light into an associated one of thewaveguides 270, 280, 290, 300, 310. One or more optical fibers maytransmit light from the light module 530 to the one or more waveguides270, 280, 290, 300, and 310. In addition, one or more interveningoptical structures may be provided between the scanning fiber, orfibers, and the one or more waveguides 270, 280, 290, 300, 310 to, forexample, redirect light exiting the scanning fiber into the one or morewaveguides 270, 280, 290, 300, 310.

A controller 560 controls the operation of the stacked waveguideassembly 260, including operation of the image injection devices 360,370, 380, 390, 400, the light source 530, and the light modulator 540.In some embodiments, the controller 560 is part of the local dataprocessing module 140. The controller 560 includes programming (e.g.,instructions in a non-transitory medium) that regulates the timing andprovision of image information to the waveguides 270, 280, 290, 300,310. In some embodiments, the controller may be a single integraldevice, or a distributed system connected by wired or wirelesscommunication channels. The controller 560 may be part of the processingmodules 140 or 150 (FIG. 2) in some embodiments.

The waveguides 270, 280, 290, 300, 310 may be configured to propagatelight within each respective waveguide by total internal reflection(TIR). The waveguides 270, 280, 290, 300, 310 may each be planar or haveanother shape (e.g., curved), with major top and bottom surfaces andedges extending between those major top and bottom surfaces. In theillustrated configuration, the waveguides 270, 280, 290, 300, 310 mayeach include out-coupling optical elements 570, 580, 590, 600, 610 thatare configured to extract light out of a waveguide by redirecting thelight, propagating within each respective waveguide, out of thewaveguide to output image information to the eye 210. Extracted lightmay also be referred to as out-coupled light and the out-couplingoptical elements light may also be referred to light extracting opticalelements. An extracted beam of light may be output by the waveguide atlocations at which the light propagating in the waveguide strikes alight extracting optical element. The out-coupling optical elements 570,580, 590, 600, 610 may be, for example, diffractive optical features,including diffractive gratings, as discussed further herein. While theout-coupling optical elements 570, 580, 590, 600, 610 are illustrated asbeing disposed at the bottom major surfaces of the waveguides 270, 280,290, 300, 310, in some embodiments they may be disposed at the topand/or bottom major surfaces, and/or may be disposed directly in thevolume of the waveguides 270, 280, 290, 300, 310, as discussed furtherherein. In some embodiments, the out-coupling optical elements 570, 580,590, 600, 610 may be formed in a layer of material that is attached to atransparent substrate to form the waveguides 270, 280, 290, 300, 310. Insome other embodiments, the waveguides 270, 280, 290, 300, 310 may be amonolithic piece of material and the out-coupling optical elements 570,580, 590, 600, 610 may be formed on a surface and/or in the interior ofthat piece of material.

Each waveguide 270, 280, 290, 300, 310 may output light to form an imagecorresponding to a particular depth plane. For example, the waveguide270 nearest the eye may deliver collimated beams of light to the eye210. The collimated beams of light may be representative of the opticalinfinity focal plane. The next waveguide up 280 may output collimatedbeams of light which pass through the first lens 350 (e.g., a negativelens) before reaching the eye 210. The first lens 350 may add a slightconvex wavefront curvature to the collimated beams so that the eye/braininterprets light coming from that waveguide 280 as originating from afirst focal plane closer inward toward the eye 210 from opticalinfinity. Similarly, the third waveguide 290 passes its output lightthrough both the first lens 350 and the second lens 340 before reachingthe eye 210. The combined optical power of the first lens 350 and thesecond lens 340 may add another incremental amount of wavefrontcurvature so that the eye/brain interprets light coming from the thirdwaveguide 290 as originating from a second focal plane that is evencloser inward from optical infinity than was light from the secondwaveguide 280.

The other waveguide layers 300, 310 and lenses 330, 320 are similarlyconfigured, with the highest waveguide 310 in the stack sending itsoutput through all of the lenses between it and the eye for an aggregatefocal power representative of the closest focal plane to the person. Tocompensate for the stack of lenses 320, 330, 340, 350 whenviewing/interpreting light coming from the world 510 on the other sideof the stacked waveguide assembly 260, a compensating lens layer 620 maybe disposed at the top of the stack to compensate for the aggregateoptical power of the lens stack 320, 330, 340, 350 below. Such aconfiguration provides as many perceived focal planes as there areavailable waveguide/lens pairings. Both the out-coupling opticalelements of the waveguides and the focusing aspects of the lenses may bestatic (i.e., not dynamic or electro-active). In some alternativeembodiments, either or both may be dynamic using electro-activefeatures.

In some embodiments, two or more of the waveguides 270, 280, 290, 300,310 may have the same associated depth plane. For example, multiplewaveguides 270, 280, 290, 300, 310 may output images set to the samedepth plane, or multiple subsets of the waveguides 270, 280, 290, 300,310 may output images set to the same plurality of depth planes, withone set for each depth plane. This can provide advantages for forming atiled image to provide an expanded field of view at those depth planes.

The out-coupling optical elements 570, 580, 590, 600, 610 may beconfigured to both redirect light out of their respective waveguides andto output this light with the appropriate amount of divergence orcollimation for a particular depth plane associated with the waveguide.As a result, waveguides having different associated depth planes mayhave different configurations of out-coupling optical elements 570, 580,590, 600, 610, which output light with a different amount of divergencedepending on the associated depth plane. In some embodiments, the lightextracting optical elements 570, 580, 590, 600, 610 may be volumetric orsurface features, which may be configured to output light at specificangles. For example, the light extracting optical elements 570, 580,590, 600, 610 may be volume holograms, surface holograms, and/ordiffraction gratings. In some embodiments, the features 320, 330, 340,350 may not be lenses; rather, they may simply be spacers (e.g.,cladding layers and/or structures for forming air gaps).

In some embodiments, the out-coupling optical elements 570, 580, 590,600, 610 are diffractive features with a diffractive efficiencysufficiently low such that only a portion of the power of the light in abeam is re-directed toward the eye 210 with each interaction, while therest continues to move through a waveguide via TIR. Accordingly, theexit pupil of the light module 530 is replicated across the waveguide tocreate a plurality of output beams carrying the image information fromlight source 530, effectively expanding the number of locations wherethe eye 210 may intercept the replicated light source exit pupil. Thesediffractive features may also have a variable diffractive efficiencyacross their geometry to improve uniformity of light output by thewaveguide.

In some embodiments, one or more diffractive features may be switchablebetween “on” states in which they actively diffract, and “off” states inwhich they do not significantly diffract. For instance, a switchablediffractive element may include a layer of polymer dispersed liquidcrystal in which microdroplets form a diffraction pattern in a hostmedium, and the refractive index of the microdroplets may be switched tosubstantially match the refractive index of the host material (in whichcase the pattern does not appreciably diffract incident light) or themicrodroplet may be switched to an index that does not match that of thehost medium (in which case the pattern actively diffracts incidentlight).

In some embodiments, a camera assembly 630 (e.g., a digital camera,including visible light and IR light cameras) may be provided to captureimages of the eye 210, parts of the eye 210, or at least a portion ofthe tissue surrounding the eye 210 to, for example, detect user inputs,extract biometric information from the eye, estimate and track the gazedirection of the eye, to monitor the physiological state of the user,etc. In some embodiments, the camera assembly 630 may include an imagecapture device and a light source to project light (e.g., IR or near-IRlight) to the eye, which may then be reflected by the eye and detectedby the image capture device. In some embodiments, the light sourceincludes light emitting diodes (“LEDs”), emitting in IR or near-IR. Insome embodiments, the camera assembly 630 may be attached to the frame80 (FIG. 2) and may be in electrical communication with the processingmodules 140 or 150, which may process image information from the cameraassembly 630 to make various determinations regarding, for example, thephysiological state of the user, the gaze direction of the wearer, irisidentification, etc. In some embodiments, one camera assembly 630 may beutilized for each eye, to separately monitor each eye.

FIG. 7A illustrates an example of exit beams output by a waveguide. Onewaveguide is illustrated (with a perspective view), but other waveguidesin the waveguide assembly 260 (FIG. 6) may function similarly. Light 640is injected into the waveguide 270 at the input surface 460 of thewaveguide 270 and propagates within the waveguide 270 by TIR. Throughinteraction with diffractive features, light exits the waveguide as exitbeams 650. The exit beams 650 replicate the exit pupil from a projectordevice which projects images into the waveguide. Any one of the exitbeams 650 includes a sub-portion of the total energy of the input light640. And in a perfectly efficient system, the summation of the energy inall the exit beams 650 would equal the energy of the input light 640.The exit beams 650 are illustrated as being substantially parallel inFIG. 7A but, as discussed herein, some amount of optical power may beimparted depending on the depth plane associated with the waveguide 270.Parallel exit beams may be indicative of a waveguide with out-couplingoptical elements that out-couple light to form images that appear to beset on a depth plane at a large distance (e.g., optical infinity) fromthe eye 210. Other waveguides or other sets of out-coupling opticalelements may output an exit beam pattern that is more divergent, asshown in FIG. 7B, which would require the eye 210 to accommodate to acloser distance to bring it into focus on the retina and would beinterpreted by the brain as light from a distance closer to the eye 210than optical infinity.

In some embodiments, a full color image may be formed at each depthplane by overlaying images in each of the component colors (e.g., threeor more component colors, such as red, green, and blue). FIG. 8illustrates an example of a stacked waveguide assembly in which eachdepth plane includes images formed using multiple different componentcolors. The illustrated embodiment shows depth planes 240 a-240 f,although more or fewer depths are also contemplated. Each depth planemay have three or more component color images associated with it,including: a first image of a first color, G; a second image of a secondcolor, R; and a third image of a third color, B. Different depth planesare indicated in the figure by different diopter powers following theletters G, R, and B. The numbers following each of these lettersindicate diopters (1/m), or inverse distance of the depth plane from auser, and each box in the figure represents an individual componentcolor image. In some embodiments, to account for differences in theeye's focusing of light of different wavelengths, the exact placement ofthe depth planes for different component colors may vary. For example,different component color images for a given depth plane may be placedon depth planes corresponding to different distances from the user. Suchan arrangement may increase visual acuity and user comfort or maydecrease chromatic aberrations.

In some embodiments, light of each component color may be output by asingle dedicated waveguide and, consequently, each depth plane may havemultiple waveguides associated with it. In such embodiments, each box inthe figure may be understood to represent an individual waveguide, andthree waveguides may be provided per depth plane so as to display threecomponent color images per depth plane. While the waveguides associatedwith each depth plane are shown adjacent to one another in this drawingfor ease of illustration, it will be appreciated that, in a physicaldevice, the waveguides may all be arranged in a stack with one waveguideper level. In some other embodiments, multiple component colors may beoutput by the same waveguide, such that, for example, only a singlewaveguide may be provided per depth plane.

With continued reference to FIG. 8, in some embodiments, G is the colorgreen, R is the color red, and B is the color blue. In some otherembodiments, other colors associated with other wavelengths of light,including yellow, magenta and cyan, may be used in addition to or mayreplace one or more of red, green, or blue. In some embodiments,features 320, 330, 340, and 350 may be active or passive optical filtersconfigured to block or selectively pass light from the ambientenvironment to the user's eyes.

References to a given color of light throughout this disclosure shouldbe understood to encompass light of one or more wavelengths within arange of wavelengths of light that are perceived by a user as being ofthat given color. For example, red light may include light of one ormore wavelengths in the range of about 620-780 nm, green light mayinclude light of one or more wavelengths in the range of about 492-577nm, and blue light may include light of one or more wavelengths in therange of about 435-493 nm.

In some embodiments, the light source 530 (FIG. 6) may be configured toemit light of one or more wavelengths outside the visual perceptionrange of the user, for example, IR or ultraviolet wavelengths. IR lightcan include light with wavelengths in a range from 700 nm to 10 μm. Insome embodiments, IR light can include near-IR light with wavelengths ina range from 700 nm to 1.5 μm. In addition, the in-coupling,out-coupling, and other light redirecting structures of the waveguidesof the display 250 may be configured to direct and emit this light outof the display towards the user's eye 210, e.g., for imaging or userstimulation applications.

With reference now to FIG. 9A, in some embodiments, light impinging on awaveguide may need to be redirected so as to in-couple the light intothe waveguide. An in-coupling optical element may be used to redirectand in-couple the light into its corresponding waveguide. FIG. 9Aillustrates a cross-sectional side view of an example of a set 660 ofstacked waveguides that each includes an in-coupling optical element.The waveguides may each be configured to output light of one or moredifferent wavelengths, or one or more different ranges of wavelengths.It will be appreciated that the stack 660 may correspond to the stack260 (FIG. 6) and the illustrated waveguides of the stack 660 maycorrespond to part of the plurality of waveguides 270, 280, 290, 300,310, except that light from one or more of the image injection devices360, 370, 380, 390, 400 is injected into the waveguides from a positionor orientation that requires light to be redirected for in-coupling.

The illustrated set 660 of stacked waveguides includes waveguides 670,680, and 690. Each waveguide includes an associated in-coupling opticalelement (which may also be referred to as a light input area on thewaveguide), with, for example, in-coupling optical element 700 disposedon a major surface (e.g., an upper major surface) of waveguide 670,in-coupling optical element 710 disposed on a major surface (e.g., anupper major surface) of waveguide 680, and in-coupling optical element720 disposed on a major surface (e.g., an upper major surface) ofwaveguide 690. In some embodiments, one or more of the in-couplingoptical elements 700, 710, 720 may be disposed on the bottom majorsurface of the respective waveguide 670, 680, 690 (particularly wherethe one or more in-coupling optical elements are reflective opticalelements). As illustrated, the in-coupling optical elements 700, 710,720 may be disposed on the upper major surface of their respectivewaveguide 670, 680, 690 (or the top of the next lower waveguide),particularly where those in-coupling optical elements are transmissiveoptical elements. In some embodiments, the in-coupling optical elements700, 710, 720 may be disposed in the body of the respective waveguide670, 680, 690. In some embodiments, as discussed herein, the in-couplingoptical elements 700, 710, 720 are wavelength selective, such that theyselectively redirect one or more wavelengths of light, whiletransmitting other wavelengths of light. While illustrated on one sideor corner of their respective waveguide 670, 680, 690, it will beappreciated that the in-coupling optical elements 700, 710, 720 may bedisposed in other areas of their respective waveguide 670, 680, 690 insome embodiments.

As illustrated, the in-coupling optical elements 700, 710, 720 may belaterally offset from one another. In some embodiments, each in-couplingoptical element may be offset such that it receives light without thatlight passing through another in-coupling optical element. For example,each in-coupling optical element 700, 710, 720 may be configured toreceive light from a different image injection device 360, 370, 380,390, and 400 as shown in FIG. 6, and may be separated (e.g., laterallyspaced apart) from other in-coupling optical elements 700, 710, 720 suchthat it substantially does not receive light from the other ones of thein-coupling optical elements 700, 710, 720.

Each waveguide also includes associated light distributing elements,with, for example, light distributing elements 730 disposed on a majorsurface (e.g., a top major surface) of waveguide 670, light distributingelements 740 disposed on a major surface (e.g., a top major surface) ofwaveguide 680, and light distributing elements 750 disposed on a majorsurface (e.g., a top major surface) of waveguide 690. In some otherembodiments, the light distributing elements 730, 740, 750 may bedisposed on a bottom major surface of associated waveguides 670, 680,690, respectively. In some other embodiments, the light distributingelements 730, 740, 750 may be disposed on both top and bottom majorsurface of associated waveguides 670, 680, 690 respectively; or thelight distributing elements 730, 740, 750, may be disposed on differentones of the top and bottom major surfaces in different associatedwaveguides 670, 680, 690, respectively.

The waveguides 670, 680, 690 may be spaced apart and separated by, forexample, gas, liquid, or solid layers of material. For example, asillustrated, layer 760 a may separate waveguides 670 and 680; and layer760 b may separate waveguides 680 and 690. In some embodiments, thelayers 760 a and 760 b are formed of low refractive index materials(that is, materials having a lower refractive index than the materialforming the immediately adjacent one of waveguides 670, 680, 690). Insome embodiments, the refractive index of the material forming thelayers 760 a, 760 b is at least 0.05, or at least 0.10, less than therefractive index of the material forming the waveguides 670, 680, 690.Advantageously, the lower refractive index layers 760 a, 760 b mayfunction as cladding layers that facilitate TIR of light through thewaveguides 670, 680, 690 (e.g., TIR between the top and bottom majorsurfaces of each waveguide). In some embodiments, the layers 760 a, 760b are formed of air. While not illustrated, it will be appreciated thatthe top and bottom of the illustrated set 660 of waveguides may includeimmediately neighboring cladding layers.

Preferably, for ease of manufacturing and other considerations, thematerial forming the waveguides 670, 680, 690 are similar or the same,and the material forming the layers 760 a, 760 b are similar or thesame. In other embodiments, the material forming the waveguides 670,680, 690 may be different between one or more waveguides, or thematerial forming the layers 760 a, 760 b may be different, while stillholding to the various refractive index relationships noted above.

With continued reference to FIG. 9A, light rays 770, 780, 790 areincident on the set 660 of waveguides. Light rays 770, 780, 790 may beinjected into the waveguides 670, 680, 690 by one or more imageinjection devices 360, 370, 380, 390, 400 (FIG. 6).

In some embodiments, the light rays 770, 780, 790 have differentproperties (e.g., different wavelengths or different ranges ofwavelengths), which may correspond to different colors. The in-couplingoptical elements 700, 710, 720 each re-direct the incident light suchthat the light propagates through a respective one of the waveguides670, 680, 690 by TIR.

For example, in-coupling optical element 700 may be configured tore-direct ray 770, which has a first wavelength or range of wavelengths.Similarly, transmitted ray 780 impinges on and is re-directed byin-coupling optical element 710, which is configured to re-direct lightof a second wavelength or range of wavelengths. Likewise, ray 790 isre-directed by in-coupling optical element 720, which is configured toselectively re-direct light of third wavelength or range of wavelengths.

With continued reference to FIG. 9A, light rays 770, 780, 790 arere-directed so that they propagate through a corresponding waveguide670, 680, 690; that is, the in-coupling optical element 700, 710, 720 ofeach waveguide re-directs light into that corresponding waveguide 670,680, 690 to in-couple light into that corresponding waveguide. The lightrays 770, 780, 790 are re-directed at angles that cause the light topropagate through the respective waveguide 670, 680, 690 by TIR. Thelight rays 770, 780, 790 propagate through the respective waveguide 670,680, 690 by TIR until interacting with the waveguide's correspondinglight distributing elements 730, 740, 750.

With reference now to FIG. 9B, a perspective view of an example of theplurality of stacked waveguides of FIG. 9A is illustrated. As notedabove, the light rays 770, 780, 790, are in-coupled by the in-couplingoptical elements 700, 710, 720, respectively, and then propagate by TIRwithin the waveguides 670, 680, 690, respectively. The light rays 770,780, 790 then interact with the light distributing elements 730, 740,750, respectively. The light distributing elements 730, 740, 750re-direct the light rays 770, 780, 790 so that they propagate towardsthe out-coupling optical elements 800, 810, and 820, respectively.

In some embodiments, the light distributing elements 730, 740, 750 areorthogonal pupil expanders (OPEs). In some embodiments, the OPEs bothre-direct light to the out-coupling optical elements 800, 810, 820 andalso expand the pupil associated with this light by sampling the lightrays 770, 780, 790 at many locations across the light distributingelements 730, 740, 750 as they propagate to the out-coupling opticalelements. In some embodiments (e.g., where the exit pupil is already ofa desired size), the light distributing elements 730, 740, 750 may beomitted and the in-coupling optical elements 700, 710, 720 may beconfigured to re-direct light directly to the out-coupling opticalelements 800, 810, 820. For example, with reference to FIG. 9A, thelight distributing elements 730, 740, 750 may be replaced without-coupling optical elements 800, 810, 820, respectively. In someembodiments, the out-coupling optical elements 800, 810, 820 are exitpupils (EPs) or exit pupil expanders (EPEs) that re-direct light out ofthe waveguides and toward a user's eye 210 (FIG. 7). The OPEs may beconfigured to increase the dimensions of the eye box in at least oneaxis and the EPEs may be configured to increase the eye box in an axiscrossing (e.g., orthogonal to) the axis of the OPEs.

Accordingly, with reference to FIGS. 9A and 9B, in some embodiments, theset 660 of waveguides includes waveguides 670, 680, 690; in-couplingoptical elements 700, 710, 720; light distributing elements (e.g., OPEs)730, 740, 750; and out-coupling optical elements (e.g., EPEs) 800, 810,820 for each component color. The waveguides 670, 680, 690 may bestacked with an air gap/cladding layer between each one. The in-couplingoptical elements 700, 710, 720 direct incident light (with differentin-coupling optical elements receiving light of different wavelengths)into a corresponding waveguide. The light then propagates at angleswhich support TIR within the respective waveguide 670, 680, 690. SinceTIR only occurs for a certain range of angles, the range of propagationangles of the light rays 770, 780, 790 is limited. The range of angleswhich support TIR may be thought of in such an example as the angularlimits of the field of view which can be displayed by the waveguides670, 680, 690. In the example shown, light ray 770 (e.g., blue light) isin-coupled by the first in-coupling optical element 700, and thencontinues to reflect back and forth from the surfaces of the waveguidewhile traveling down the waveguide, with the light distributing element(e.g., OPE) 730 progressively sampling it to create additionalreplicated rays which are directed toward the out-coupling opticalelement (e.g., EPE) 800, in a manner described earlier. The light rays780 and 790 (e.g., green and red light, respectively) will pass throughthe waveguide 670, with light ray 780 impinging on and being in-coupledby in-coupling optical element 710. The light ray 780 then propagatesdown the waveguide 680 via TIR, proceeding on to its light distributingelement (e.g., OPE) 740 and then the out-coupling optical element (e.g.,EPE) 810. Finally, light ray 790 (e.g., red light) passes through thewaveguides 670, 680 to impinge on the light in-coupling optical element720 of the waveguide 690. The light in-coupling optical element 720in-couples the light ray 790 such that the light ray propagates to lightdistributing element (e.g., OPE) 750 by TIR, and then to theout-coupling optical element (e.g., EPE) 820 by TIR. The out-couplingoptical element 820 then finally out-couples the light ray 790 to theuser, who also receives the out-coupled light from the other waveguides670, 680.

FIG. 9C illustrates a top-down plan view of an example of the pluralityof stacked waveguides of FIGS. 9A and 9B. As illustrated, the waveguides670, 680, 690, along with each waveguide's associated light distributingelement 730, 740, 750 and associated out-coupling optical element 800,810, 820, may be vertically aligned. However, as discussed herein, thein-coupling optical elements 700, 710, 720 are not vertically aligned;rather, the in-coupling optical elements may be non-overlapping (e.g.,laterally spaced apart as seen in the top-down view). Thisnon-overlapping spatial arrangement may facilitate the injection oflight from different sources into different waveguides on a one-to-onebasis, thereby allowing a specific light source to be uniquely opticallycoupled to a specific waveguide. In some embodiments, arrangementsincluding non-overlapping spatially separated in-coupling opticalelements may be referred to as a shifted pupil system, and thein-coupling optical elements within these arrangements may correspond tosub pupils.

FIG. 10 is a perspective view of an example AR eyepiece waveguide stack1000. The eyepiece waveguide stack 1000 may include a world-side coverwindow 1002 and an eye-side cover window 1006 to protect one or moreeyepiece waveguides 1004 positioned between the cover windows. In otherembodiments, one or both of the cover windows 1002, 1006 may be omitted.As already discussed, the eyepiece waveguides 1004 may be arranged in alayered configuration. The eyepiece waveguides 1004 may be coupledtogether, for instance, with each individual eyepiece waveguide beingcoupled to one or more adjacent eyepiece waveguides. In someembodiments, the waveguides 1004 may be coupled together with an edgeseal (such as the edge seal 1108 shown in FIG. 11) such that adjacenteyepiece waveguides 1004 are not in direct contact with each other.

Each of the eyepiece waveguides 1004 can be made of a substrate materialthat is at least partially transparent, such as glass, plastic,polycarbonate, sapphire, etc. The selected material may have an index ofrefraction above 1.4, for example, or above 1.6, or above 1.8, tofacilitate light guiding. The thickness of each eyepiece waveguidesubstrate may be, for example, 325 microns or less, though otherthicknesses can also be used. Each eyepiece waveguide can include one ormore in-coupling regions, light distributing regions, image expandingregions, and out-coupling regions, which may be made up of diffractivefeatures formed on or in each waveguide substrate 902.

Although not illustrated in FIG. 10, the eyepiece waveguide stack 1000can include a physical support structure for supporting it in front of auser's eyes. In some embodiments, the eyepiece waveguide stack 1000 ispart of a head-mounted display system 60, as illustrated in FIG. 2. Ingeneral, the eyepiece waveguide stack 1000 is supported such that anout-coupling region is directly in front of a user's eye. It should beunderstood that FIG. 10 illustrates only the portion of the eyepiecewaveguide stack 1000 which corresponds to one of the user's eyes. Acomplete eyepiece may include a mirror image of the same structure, withthe two halves possibly separated by a nose piece.

In some embodiments, the eyepiece waveguide stack 1000 can project colorimage data from multiple depth planes into the user's eyes. The imagedata displayed by each individual eyepiece waveguide 1004 in theeyepiece 1000 may correspond to a selected color component of the imagedata for a selected depth plane. For example, since the eyepiecewaveguide stack 1000 includes six eyepiece waveguides 1004, it canproject color image data (e.g., made up of red, green, and bluecomponents) corresponding to two different depth planes: one eyepiecewaveguide 1004 per color component per depth plane. Other embodimentscan include eyepiece waveguides 1004 for more or fewer color componentsand/or more or fewer depth planes.

FIG. 11 is a cross-sectional view of a portion of an example eyepiecewaveguide stack 1100 with an edge seal structure 1108 for supportingeyepiece waveguides 1104 in a stacked configuration. The edge sealstructure 1108 aligns the eyepiece waveguides 1104 and separates themfrom one another with air space or another material disposed between.Although not illustrated, the edge seal structure 1108 can extend aroundthe entire perimeter of the stacked waveguide configuration. In FIG. 11,the separation between each eyepiece waveguide is 0.027 mm, though otherdistances are also possible.

In the illustrated embodiment, there are two eyepiece waveguides 1104designed to display red image data, one for a 3 m depth plane and theother for a 1 m depth plane. (Again, the divergence of the beams oflight output by an eyepiece waveguide 1104 can make the image dataappear to originate from a depth plane located at a particulardistance.) Similarly, there are two eyepiece waveguides 1104 designed todisplay blue image data, one for a 3 m depth plane and the other for a 1m depth plane, and two eyepiece waveguides 1104 designed to displaygreen image data, one for a 3 m depth plane and the other for a 1 mdepth plane. Each of these six eyepiece waveguides 1104 is illustratedas being 0.325 mm thick, though other thicknesses are also possible.

A world-side cover window 1102 and an eye-side cover window 1106 arealso shown in FIG. 11. These cover windows can be, for example, 0.330 mmthick. When accounting for the thickness of the six eyepiece waveguides1104, the seven air gaps, the two cover windows 1102, 1106, and the edgeseal 1108, the total thickness of the illustrated eyepiece waveguidestack 1100 is 2.8 mm.

FIGS. 12A and 12B illustrate top views of an eyepiece waveguide 1200 inoperation as it projects an image toward a user's eye 210. The image canfirst be projected from an image plane 1207 toward an entrance pupil1208 of the eyepiece waveguide 1200 using a projection lens 1210 or someother projector device. Each image point (e.g., an image pixel or partof an image pixel) has a corresponding input beam of light (e.g., 1202a, 1204 a, 1206 a) which propagates in a particular direction at theentrance pupil 1208 (e.g., at a particular angle with respect to theoptical axis of the projector lens 1210). Although illustrated as rays,the input beams of light 1202 a, 1204 a, 1206 a may be, for example,collimated beams with diameters of a few millimeters or less when theyenter the eyepiece waveguide 1200.

In FIGS. 12A and 12B, a middle image point corresponds to input beam1204 a, which is illustrated with a solid line. Input beam 1202 a, whichis illustrated with a dash-dot line, corresponds to an image pointdisplaced to one side of the middle image point, while input beam 1206a, which is illustrated with a dashed line, corresponds to an imagepoint displaced to the other side. For clarity of illustration, onlythree input beams 1202 a, 1204 a, 1206 a are shown at the entrance pupil1208, though a typical input image will include many input beams whichcorrespond to different image points. And the input beams will propagateat a range of angles with respect to the optical axis, both in thex-direction and the y-direction.

There is a unique correspondence between the various propagation anglesof the input beams (e.g., 1202 a, 1204 a, 1206 a) at the entrance pupil1208 and the respective image points at the image plane 1207. Theeyepiece waveguide 1200 can be designed to in-couple the input beams(e.g., 1202 a, 1204 a, 1206 a), replicate them in a distributed mannerthrough space, and guide them to form an exit pupil 1210, which islarger than the entrance pupil 1208 and is made up of the replicatedbeams, all while substantially maintaining the correspondence betweenimage points and beam angles. The eyepiece waveguide 1200 can convert agiven input beam of light (e.g., 1202 a), which propagates at aparticular angle, into many replicated beams (e.g., 1202 b) which areoutput across the exit pupil 1210 at an angle that is substantiallyuniquely correlated with that particular input beam and itscorresponding image point. Accordingly, the eyepiece waveguide 1200 canperform pupil expansion while maintaining the relative angularrelationships of the beams which make up the projected image.

As shown in FIGS. 12A and 12B, input beam of light 1204 a, correspondingto the middle image point at the image plane 1207, is converted into aset of replicated output beams 1204 b, shown with solid lines, which arealigned with an optical axis perpendicular to the exit pupil 1210 of theeyepiece waveguide 1200. Input beam of light 1202 a is converted into aset of replicated output beams 1202 b, shown with dash-dot lines, whichexit the eyepiece waveguide 1200 at a propagation angle such that theyappear to have originated from one side of the user's field of view,while input beam of light 1206 a is converted into a set of replicatedoutput beams 1206 b, shown with dashed lines, which exit the eyepiecewaveguide 1200 at a propagation angle such that they appear to haveoriginated from the other side of the user's field of view. The greaterthe range of input beam angles and/or output beam angles, the greaterthe field of view (FOV) of the eyepiece waveguide 1200.

For each image, there are sets of replicated output beams (e.g., 1202 b,1204 b, 1206 b)—one set of replicated beams per image point—which areoutput across the exit pupil 1210 at different angles. The output beams(e.g., 1202 b, 1204 b, 1206 b) can each be collimated. The set of outputbeams corresponding to a given image point may consist of beams whichpropagate along parallel paths (as shown in FIG. 12A) or diverging paths(as shown in FIG. 12B). In either case, the specific propagation angleof the set of replicated output beams depends on the location of thecorresponding image point at the image plane 1207. FIG. 12A illustratesthe case where each set of output beams (e.g., 1202 b, 1204 b, 1206 b)consists of beams which propagate along parallel paths. This results inthe image being projected so as to appear to have originated fromoptical infinity. This is represented in FIG. 12A by the faint linesextending from the peripheral output beams 1202 b, 1204 b, 1206 b towardoptical infinity on the world-side of the eyepiece waveguide 1200(opposite the side where the user's eye 210 is located). FIG. 12Billustrates the case where each set of output beams (e.g., 1202 b, 1204b, 1206 b) consists of beams which propagate along diverging paths. Thisresults in the image being projected so as to appear to have originatedfrom a distance closer than optical infinity. This is represented inFIG. 12B by the faint lines extending from the peripheral output beams1202 b, 1204 b, 1206 b toward points on the world-side of the eyepiecewaveguide 1200.

Again, each set of replicated output beams (e.g., 1202 b, 1204 b, 1206b) has a propagation angle that corresponds to a particular image pointat the image plane 1207. In the case of a set of replicated output beamswhich propagate along parallel paths (see FIG. 12A), the propagationangles of all the beams are the same. In the case of a set of replicatedoutput beams which propagate along diverging paths, however, theindividual output beams can propagate at different angles, but thoseangles are related to one another in that they appear to have originatedfrom a common point along the axis of the set of beams (See FIG. 12B).It is this axis which defines the angle of propagation for the set ofdiverging output beams and which corresponds to a particular image pointat the image plane 1207.

Example Eyepiece Waveguides

FIG. 13A illustrates a front view (in the as-worn position) of one halfof an example eyepiece waveguide 1300 for a VR/AR/MR system. Theeyepiece waveguide 1300 can include an input coupler region 1310, anupper orthogonal pupil expander (OPE) region 1320 a, a lower orthogonalpupil expander (OPE) region 1320 b, and an exit pupil expander (EPE)region 1330. In some embodiments, the eyepiece waveguide 1300 can alsoinclude an upper spreader region 1340 a, and a lower spreader region1340 b. The eyepiece waveguide 1300 is made of a substrate material thatis at least partially transparent. For example, the eyepiece waveguide1300 can be made of a glass, plastic, polycarbonate, sapphire, etc.substrate 1302. The selected material may have an index of refractionabove 1, more preferably a relatively high index of refraction above1.4, or more preferably above 1.6, or most preferably above 1.8 tofacilitate light guiding. The thickness of the substrate 1302 may be,for example, 325 microns or less. Each of the aforementioned regions ofthe eyepiece waveguide 1300 can be made by forming one or morediffractive structures on or in the eyepiece waveguide substrate 1302.The specific diffractive structures may vary from region to region.

Although not illustrated in FIG. 13A, the eyepiece waveguide 1300 caninclude a physical support structure for supporting the eyepiecewaveguide in front of a user's eyes. In some embodiments, the eyepiecewaveguide 1300 is part of a head-mounted display, as illustrated in FIG.2. In general, the eyepiece waveguide 1300 is supported such that theEPE region 1330 is directly in front of a user's eye. It should beunderstood that FIG. 13A illustrates only one half of the eyepiecewaveguide 1300, corresponding to one of the user's eyes. A completeeyepiece waveguide typically also includes a mirror image of the samestructure illustrated in FIG. 13A (e.g., with the respective inputcoupler regions 1310 towards the temples of the user's head and therespective EPE regions 1330 in front of the user's eyes and possiblyseparated by a nose piece). The two halves can be part of the samesubstrate 1302 or separate substrates.

As shown in FIGS. 10 and 11, in some embodiments, an eyepiece caninclude multiple eyepiece waveguides 1300 made of multiple substrates1302 that are stacked together (separated by a cladding layer). Eachsubstrate 1302 can be as illustrated in FIG. 13A and can be designed asa waveguide to project image data into the eye. In some embodiments, theimage data displayed by each eyepiece waveguide 1300 in the stackcorresponds to a selected color component of the image datacorresponding to a selected depth plane. For example, an eyepiece thatprojects color image data (e.g., made up of red, green, and bluecomponents) corresponding to three different depth planes may include atotal of nine eyepiece waveguides 1300 stacked together: one eyepiecewaveguide 1300 for each color component of the image data for each ofthree depth planes.

FIG. 13B illustrates some of the diffractive optical features of theeyepiece waveguide 1300 which cause image data projected into theeyepiece waveguide at the input coupler region 1310 to propagate throughthe eyepiece waveguide and to be projected out toward the user's eyefrom the EPE region 1330. Generally speaking, image data is projectedinto the eyepiece waveguide 1300 via beams of light which travelapproximately in the illustrated z-direction (but the amount of angularvariation may depend upon the FOV of the image data) and are incident onthe input coupler region 1310 from outside of the substrate 1302. Theinput coupler region 1310 includes diffractive optical features whichredirect the input beams of light such that they propagate inside thesubstrate 1302 of the eyepiece waveguide 1300 via total internalreflection. In some embodiments, the input coupler region 1310 issymmetrically located between upper and lower OPE regions 1320. Theinput coupler region 1310 divides and redirects the input light towardsboth of these OPE regions 1320.

The OPE regions 1320 include diffractive optical features which canperform at least two functions: first, they can perform pupil expansionby spatially replicating each input beam of light at many locationsalong the y-direction to form many spaced apart parallel beams; second,they can diffract the replicated beams of light on paths generallytoward the EPE region 1330.

The EPE region 1330 likewise includes diffractive optical features whichcan perform at least two functions: first, they can replicate beams atmany locations along another direction (e.g., a direction generallyorthogonal to the one in which beams are replicated by the OPE regions1320); second, they can diffract the beams of light coming from the OPEregions 1320 such that they exit the substrate 1302 of the eyepiecewaveguide 1300 and propagate toward the user's eye. The diffractiveoptical features of the EPE region 1330 may also impart a degree ofoptical power to the exiting beams of light to make them appear as ifthey originate from a desired depth plane, as discussed elsewhereherein. The eyepiece waveguide 1300 can have the property that the angleof exit at which light beams are output by the EPE region 1330 isuniquely correlated with the angle of entrance of the correspondinginput beam at the input coupler region 1310, thereby allowing the eye tofaithfully reproduce the input image data.

The optical operation of the eyepiece waveguide 1300 will now bedescribed in more detail. First, image data is projected into theeyepiece waveguide 1300 at the input coupler region 1310 from one ormore input devices. The input device(s) can include, for example,spatial light modulator projectors (located in front of, or behind, theeyepiece waveguide 1300 with respect to the user's face). In someembodiments, the input device(s) may use liquid crystal display (LCD)technology, liquid crystal on silicon (LCoS) technology, digital lightprocessing (DLP) technology, or fiber scanned display (FSD) technology,though others can also be used. Each input device can project one ormore beams of light onto a sub-portion of the input coupler region 1310.As discussed elsewhere herein, each substrate 1302 can act as awaveguide to direct a given color component for a given depth plane ofimage data into the user's eye. A different sub-portion of the inputcoupler region 1310 can be used to input image data for each of themultiple stacked eyepiece waveguides 1300 that make up the eyepiece.This can be accomplished by, for each eyepiece waveguide 1300, providingappropriate diffractive optical features at the sub-portion of the inputcoupler region 1310 which has been set aside for inputting image datainto the substrate 1302 of that eyepiece waveguide 1300 (e.g., as shownin FIGS. 9A-9C). For example, one substrate 1302 may have diffractivefeatures provided in the center of its input coupler region 1310, whileothers may have diffractive features provided at the periphery of theirrespective input coupler regions at, for example, the 3 o'clock or 9o'clock positions. Thus, the input image data intended for each eyepiecewaveguide 1300 can be aimed by the projector at the correspondingsub-portion of the input coupler region 1310 such that the correct imagedata is coupled into the correct substrate 1302 without being coupledinto the other substrates.

The projector may be provided such that the input beams of lightapproach the input coupler region 1310 of a substrate 1302 generallyalong the illustrated z-direction (though there will be some angulardeviation, given that light beams corresponding to different points ofan input image will be projected at different angles). The input couplerregion 1310 of any given substrate 1302 includes diffractive opticalfeatures which redirect the input beams of light at appropriate anglesto propagate within the substrate 1302 of the eyepiece waveguide 1300via total internal reflection. As shown by magnified view 1312, in someembodiments the diffractive optical features of the input coupler region1310 may form a diffraction grating made up of many lines which extendhorizontally in the illustrated x-direction and periodically repeatvertically in the illustrated y-direction. In some embodiments, thelines may be etched into the substrate 1302 of the eyepiece waveguide1300 and/or they may be formed of material deposited onto the substrate1302. For example, the input coupler grating (ICG) may comprise linesetched into the back surface of the substrate (opposite the side whereinput light beams enter) and then covered with sputtered-on reflectivematerial, such as metal. In such embodiments, the input coupler gratingacts in reflection mode, though other designs can use a transmissionmode. The input coupler grating can be any of several types, including asurface relief grating, binary surface relief structures, a volumeholographic optical element (VHOE), a switchable polymer dispersedliquid crystal grating, etc. The period, duty cycle, depth, profile,etc. of the lines can be selected based on the wavelength of light forwhich the substrate is designed, the desired diffractive efficiency ofthe grating, and other factors.

Input light which is incident upon this input coupler diffractiongrating is split and redirected both upward in the +y direction towardthe upper OPE region 1320 a and downward in the −y direction toward thelower OPE region 1320 b. Specifically, the input light which is incidentupon the diffraction grating of the input coupler region 1310 isseparated into positive and negative diffractive orders, with thepositive diffractive orders being directed upward toward the upper OPEregion 1320 a and the negative diffractive orders being directeddownward toward the lower OPE region 1320 b, or vice versa. In someembodiments, the diffraction grating at the input coupler region 1310 isdesigned to primarily couple input light into the +1 and −1 diffractiveorders. (The diffraction grating can be designed so as to reduce oreliminate the 0^(th) diffractive order and higher diffractive ordersbeyond the first diffractive orders. This can be accomplished by, forexample, appropriately shaping the profile of each line.)

As shown in FIG. 13A, light beams 1324 a and 1324 b respectivelyillustrate the paths along which input beams corresponding to the fourcorners of an input image projected at the 9 o'clock position of theinput coupler region 1310 are re-directed toward the upper OPE region1320 a and the lower OPE region 1320 b. Similarly, light beams 1326 aand 1326 b respectively illustrate the paths along which input beamscorresponding to the four corners of an input image projected at the 3o'clock position of the input coupler region 1310 are re-directed towardthe upper OPE region 1320 a and the lower OPE region 1320 b.

The upper OPE region 1320 a and the lower OPE region 1320 b also includediffractive optical features. In some embodiments, these diffractiveoptical features are lines formed on or in the substrate 1302 of theeyepiece waveguide 1300. The period, duty cycle, depth, profile, etc. ofthe lines can be selected based on the wavelength of light for which thesubstrate is designed, the desired diffractive efficiency of thegrating, and other factors. The specific shapes of the OPE regions 1320a, 1320 b can vary, but in general may be determined based on what isneeded to accommodate beams of light corresponding to the corners of theinput image data, and all the beams of light in between, so as toprovide a full view of the input image data.

As already mentioned, one purpose of these diffraction gratings in theOPE regions 1320 a, 1320 b is to replicate each input light beam at manyspatial locations to produce multiple spaced apart parallel light beams.This can be accomplished by designing the OPE diffraction gratings tohave relatively low diffractive efficiency (e.g., less than 10%) suchthat, with each interaction of the beam with the grating as it reflectsback and forth between the front and back surfaces of the substrate 1302via TIR, the grating re-directs (e.g., via 1st order diffraction) only adesired portion of the power of the light beam while the remainingportion continues to propagate in the same direction within the plane ofthe eyepiece waveguide 1300 (e.g., via 0th order diffraction). (Oneparameter which can be used to influence the diffractive efficiency ofthe grating is the etch depth of the lines.) Another purpose of thediffraction gratings in the OPE regions 1320 a, 1320 b is to directthose replicated light beams along paths generally toward the EPE region1330. That is, every time a light beam interacts with the OPEdiffraction grating, a portion of its power will be diffracted towardthe EPE region 1330 while the remaining portion of its power willcontinue to transmit within the OPE region in the same direction beforeonce again interacting with the grating, where another portion of itspower is deflected toward the EPE region and so on. In this way, eachinput light beam is divided into multiple parallel light beams which aredirected along paths generally toward the EPE region 1330. This isillustrated in FIG. 13C.

The orientation of the OPE diffraction gratings is slanted with respectto light beams arriving from the input coupler region 1310 so as tore-direct those light beams generally toward the EPE region 1330. Thespecific angle of the slant may depend upon the layout of the variousregions of the eyepiece waveguide 1300. In the eyepiece waveguideembodiment illustrated in FIGS. 13A and 13B, the upper OPE region 1320 aextends in the +y-direction, while the lower OPE region 1320 b extendsin the −y-direction, such that they are oriented 180° apart. Meanwhile,the EPE region 1330 is located at 90° with respect to the axis of theOPE regions 1320 a, 1320 b. Therefore, in order to re-direct light fromthe OPE regions 1320 a, 1320 b toward the EPE region 1330, thediffraction gratings of the OPE regions may be oriented at about +/−45°with respect to the illustrated x-axis. Specifically, as shown bymagnified view 1322 a, the diffraction grating of the upper OPE region1320 a may consist of lines oriented at approximately +45° to thex-axis. Meanwhile, as shown by the magnified view 1322 b, thediffraction grating of the lower OPE region 1320 b may consist of linesoriented at approximately −45° to the x-axis.

FIG. 13C is a three-dimensional illustration of the optical operation ofthe OPE regions shown in FIG. 13B. FIG. 13C shows the input couplerregion 1310 and the upper OPE region 1320 a from FIG. 13B, both on theside of the substrate 1302 that is closer to the viewer. The diffractiveoptical features of the input coupler region 1310 and the upper OPEregion 1320 a cannot be seen because they are microscopic. In this case,a single input beam 1311 is illustrated, but an image will be made up ofmany such input beams propagating through the eyepiece waveguide 1300 atslightly different angles. The input beam 1311 enters the upper OPEregion 1320 a from the input coupler region 1310. The input beam 1311then continues to propagate through the eyepiece waveguide 1300 viatotal internal reflection, repeatedly reflecting back and forth betweenits surfaces. This is represented in FIG. 13C by the zig-zagging in theillustrated propagation of each beam.

When the input beam 1311 interacts with the diffraction grating formedin the upper OPE region 1320 a, a portion of its power is diffractedtoward the EPE region 1330, while another portion of its power continuesalong the same path through the upper OPE region 1320 a. As alreadymentioned, this is due in part to the relatively low diffractiveefficiency of the grating. Further, beams diffracted toward the EPEregion 1330 may re-encounter the grating of the upper OPE region 1320 aand portions of their power may diffract back into the originaldirection of propagation of the input beam 1311, while other portions oftheir power may continue on toward the EPE region. The paths of some ofthese beams are indicated in FIG. 13C by arrows. The effect is that thespatial extent of the light is expanded since the input beam isreplicated at many locations as it propagates through the upper OPEregion 1320 a. This is evident from FIG. 13C, which shows that the inputbeam 1311 is replicated into many light beams ultimately travelinggenerally in the x-direction toward the EPE region 1330.

With reference back to FIG. 13B, it is advantageous that the inputcoupler region 1310 be located between two OPE regions because thisallows the eyepiece waveguide 1300 to efficiently make use of lightdiffracted into the positive and negative diffractive order(s) at theinput coupler region 1310, as one OPE region receives one or morepositive diffractive order(s) and the other OPE region receives one ormore negative diffractive order(s) from the input coupler region 1310.The light from the positive and negative diffractive orders can then berecombined at the EPE region 1330 and out-coupled to the user's eye.Although the position of the input coupler region 1310 between the upperand lower OPE regions 1320 a, 1320 b is advantageous in this regard, itcan result in the input coupler region 1310 effectively shadowing thecentral portion of the EPE region 1330. That is, because input beams areseparated into positive and negative diffractive orders by the inputcoupler and are first directed in the +y direction or the −y directionbefore being re-directed in the +x direction toward the EPE region 1330,fewer light beams may reach the central portion of the EPE region whichis located directly to the left of the input coupler region 1310 inFIGS. 13A and 13B. This may be undesirable because if the center of theEPE region 1330 is aligned with the user's eye, then fewer light beamsmay ultimately be directed to the user's eye from the central portion ofthe EPE region 1330 due to this shadowing effect which is caused by theposition of the input coupler region 1310 between the OPE regions 1320.As a solution to this, the eyepiece waveguide 1300 can also includeupper and lower spreader regions 1340 a, 1340 b. These spreader regionscan re-direct light beams from the OPE regions so as to fill in thecentral portion of the EPE region 1330. The upper and lower spreaderregions 1340 a, 1340 b accomplish this task with diffractive featureswhich are illustrated in FIG. 13B.

As shown in magnified view 1342 a, the upper spreader region 1340 a caninclude a diffraction grating whose grating lines are formed atapproximately −45° to the x-axis, generally orthogonal to the gratinglines in the neighboring upper OPE region 1320 a from which the upperspreader region 1340 a primarily receives light Like the OPE gratings,the efficiency of the gratings in the spreader regions can be designedsuch that only a portion of the power of each light beam is re-directedduring each interaction with the grating. Due to the orientation of thediffraction grating lines in the upper spreader region 1340 a, lightbeams from the upper OPE region 1320 a are re-directed somewhat in the−y-direction before continuing on in the +x-direction toward the EPEregion 1330. Thus, the upper spreader region 1340 a helps to increasethe number of light beams which reach the central portion of the EPEregion 1330, notwithstanding any shadowing caused by the position of theinput coupler region 1310 with respect to the EPE region 1330.Similarly, as shown in magnified view 1342 b, the lower spreader region1340 b can include grating lines which are formed at approximately +45°to the x-axis, generally orthogonal to the grating lines in theneighboring lower OPE region 1320 b from which the lower spreader region1340 b primarily receives light. The diffraction grating lines in thelower spreader region 1340 b cause light beams from the lower OPE region1320 b to be re-directed somewhat in the +y direction before continuingon in the +x direction toward the EPE region 1330. Thus, the lowerspreader region 1340 b also helps to increase the number of light beamswhich reach the central portion of the EPE region 1330.

Light beams from the OPE regions 1320 a, 1320 b and the spreader regions1340 a, 1340 b propagate through the substrate 1302 of the eyepiecewaveguide 1300 until ultimately reaching the EPE region 1330. The EPEregion 1330 can include diffractive optical features which re-direct thelight beams out of the eyepiece waveguide 1300 and toward the user'seye. As shown in magnified view 1332, the diffractive optical featuresof the EPE region 1330 can be vertical grating lines which extend in they-direction and exhibit periodicity in the x-direction. Alternatively,as shown in FIG. 14, the lines of the diffraction grating in the EPEregion 1330 can be somewhat curved in order to impart optical power tothe image data. The period, duty cycle, depth, profile, etc. of thelines can be selected based on the wavelength of light for which thesubstrate is designed, the desired diffractive efficiency of thegrating, and other factors. A portion of the power of each light beam isre-directed out of the substrate 1302 of the eyepiece waveguide 1300 asa result of each interaction with the grating in the EPE region 1330.The specific angle at which each output beam exits the EPE region 1330of the eyepiece waveguide 1300 is determined by the angle of incidenceof the corresponding input beam at the input coupler region 1310.

FIG. 14A illustrates an embodiment of an eyepiece waveguide 1400 whichincludes an input coupler region 1410 with a crossed diffractiongrating. The eyepiece waveguide 1400 is formed of a substrate 1402 andincludes the input coupler region 1410, an upper OPE region 1420 a, alower OPE region 1420 b, and an EPE region 1430. Except where notedotherwise, the eyepiece waveguide 1400 shown in FIG. 14 can functionsimilarly to the eyepiece waveguide 1300 illustrated in FIGS. 13A-13C.The design of the eyepiece waveguide 1400 represents another way toincrease the amount of light that is directed toward the central portionof the EPE region 1430 (located directly to the left of the inputcoupler region 1410) without necessarily using the types of spreaderregions 1340 a, 1340 b discussed with respect to FIGS. 13A-13C.

A principal difference between the eyepiece waveguide 1400 in FIG. 14A,as compared to the eyepiece waveguide 1300 in FIGS. 13A-13C, is thedesign of the input coupler region 1410. In the eyepiece waveguide 1300shown in FIGS. 13A-13C, the input coupler region 1310 was designed so asto re-direct input light primarily only to the upper and lower OPEregions 1320 a, 1320 b. In contrast, the input coupler region 1410 shownin FIG. 14A is designed to direct input light both to the upper andlower OPE regions 1420 a, 1420 b and directly to the EPE region 1430.This can be accomplished by using a crossed diffraction grating in theinput coupler region 1410.

FIG. 14B is a perspective view of an example embodiment of the inputcoupler region 1410 made up of a crossed diffraction grating. Thecrossed grating can be thought of as the superposition of twodiffraction gratings with different orientations. The first diffractiongrating can be formed similarly to the one illustrated with respect toFIGS. 13A-13C. Namely, it can consist of lines extending in thex-direction and repeating periodically in the y-direction. This firstdiffraction grating splits input light into positive and negativediffractive orders which are respectively directed toward the upper andlower OPE regions 1420 a, 1420 b. The first diffraction grating can havea first diffractive efficiency to control the proportion of the power ofthe input light which it re-directs toward the OPE regions 1420 a, 1420b.

The second diffraction grating can consist of lines extending in they-direction and repeating periodically in the x-direction. In otherwords, the second diffraction grating can be oriented at approximately90° to the first diffraction grating. This orientation of the seconddiffraction grating causes input beams of light to be re-directed towardthe EPE region 1430, which in this embodiment is located in a directionsubstantially 90° from the directions in which the OPE regions 1420 a,1420 b are located with respect to the input coupler region 1410,without first passing through the OPE regions. (The second diffractiongrating could also have other orientations depending on the direction inwhich the EPE region 1430 is located in other embodiments.) The seconddiffraction grating can be designed to have a second diffractiveefficiency which may be different from that of the first diffractiongrating. In some embodiments, the second diffraction grating can bedesigned to be less efficient than the first diffraction grating. (Thiscan be accomplished by, for example, making the lines of the seconddiffraction grating shallower than those of the first diffractiongrating, as shown in FIG. 14B.) Thus, most of the power of the inputlight is re-directed toward the upper and lower OPE regions 1420 a, 1420b by the first diffraction grating (represented by light beams 1412 a,1412 b), while a lesser portion of the power of the input light isre-directed directly toward the EPE region 1430 by the seconddiffraction grating (represented by light beam 1414). Because the inputcoupler region 1410 re-directs some of the power of the input lightdirectly toward the EPE region 1430, such that it does not first passthrough the OPE regions 1420, the aforementioned shadowing of thecentral portion of the EPE region by the input coupler region can bereduced.

FIG. 15A illustrates an embodiment of an eyepiece waveguide 1500 withupper and lower OPE regions which are angled toward the EPE region 1530to provide a more compact form factor. The eyepiece waveguide 1500 isformed of a substrate 1502 and includes an input coupler region 1510, anupper OPE region 1520 a, a lower OPE region 1520 b, and an EPE region1530. Except where noted otherwise, the eyepiece waveguide 1500 shown inFIG. 15A can function similarly to the eyepiece waveguide 1300illustrated in FIGS. 13A-13C.

A principal difference between the eyepiece waveguide 1500 in FIG. 15A,as compared to the eyepiece waveguide 1300 in FIGS. 13A-13C, is that theOPE regions 1520 a, 1520 b are angled toward the EPE region 1530. In theembodiment shown in FIG. 15A, each OPE region is tilted from the y-axisby about 30°. Thus, rather than being separated by about 180°, as in theembodiment illustrated in FIGS. 13A-13B, the upper OPE region 1520 a andthe lower OPE region 1520 b are separated by about 120°. While theprecise amount of angling of the OPE regions 1520 a, 1520 b toward theEPE region can vary (e.g., up to 60°), in general such angling may allowthe eyepiece waveguide 1500 to achieve a more compact design. This canbe advantageous because it may allow the head-mounted display of aVR/AR/MR system to be made less bulky.

The design of the diffractive features in the input coupler region 1510can be changed to so as to match the angles at which input beams oflight are launched into the substrate 1502 of the eyepiece waveguide1500 such that they correspond with the directions in which the OPEregions 1520 a, 1520 b are located with respect to the input couplerregion 1510. An example embodiment of the diffractive features of theinput coupler region 1510 is shown in the magnified view 1512 in FIG.15B.

FIG. 15B illustrates an example embodiment of the diffractive opticalfeatures of the input coupler region 1510 of the eyepiece waveguide 1500shown in FIG. 15A. In the illustrated embodiment, the input couplerregion 1510 has a plurality of diffractive features, or light scatteringfeatures, 1514 (e.g., indentations, protrusions, etc.) laid out in ahexagonal lattice 1516. (Note: the dotted lines around each diffractivefeature 1514 are intended to illustrate the hexagonal lattice 1516, notnecessarily to correspond to any physical structure along the dottedlines.) The hexagonal lattice 1516 of the diffractive features causesthe input beams of light that are incident on the input coupler regionto be launched into the substrate 1502 of the eyepiece waveguide 1500 inmultiple directions at 60° intervals. Thus, as shown in FIG. 15A, afirst set of input beams are launched towards the upper OPE region 1520a at approximately 60° to the x-axis, a second set of input beams arelaunched toward the lower OPE region 1520 b at approximately −60° to thex-axis, and a third set of input beams are launched directly toward theEPE region 1530 generally along the x-axis. Other tessellatedconfigurations can also be used, depending on the shape of the eyepiecewaveguide 1500 and the direction(s) from the input coupler region 1510to the OPE region(s). The specific shape of the diffractive features1514 determines the efficiency with which light is re-directed into eachof these directions. In the illustrated embodiment, each of thediffractive features 1514 is a rhombus, but other shapes are alsopossible. In addition, the diffractive features 1514 can be single ormulti-leveled.

In some embodiments, the diffractive features of the input couplerregion 1510 are etched into the back surface of the substrate 1502 (onthe opposite side from where input beams enter the substrate 1502 froman input device). The etched diffractive features on the back surface ofthe substrate 1502 can then be coated with a reflective material. Inthis way, input beams of light enter the front surface of the substrateand diffract from the diffractive features on the back surface such thatthe diffractive features operate in a reflection mode. The upper OPEregion 1520 a and the lower OPE region 1520 b also include diffractiveoptical features as before. The diffractive features of the upper OPEregion 1520 a are illustrated in magnified view 1522 in FIG. 15C.

FIG. 15C illustrates an example embodiment of the diffractive opticalfeatures of the OPE region 1520 a of the eyepiece waveguide 1500 shownin FIG. 15A. As was the case with the diffractive features of the OPEregions in the eyepiece waveguide 1300 shown in FIGS. 13A and 13B, thediffractive features of the OPE regions 1520 a, 1520 b of the eyepiecewaveguide 1500 shown in FIG. 15A are likewise a periodically repeatingpattern of lines which form a diffraction grating. In this case,however, the angle at which the lines are oriented has been adjusted inview of the slanted orientation of the OPE region 1520 a so as to stillre-direct beams of light toward the EPE region 1530. Specifically, thelines of the diffraction grating in the upper OPE region 1520 a areoriented at approximately +30° with respect to the x-axis. Similarly,the lines of the diffraction grating in the lower OPE region 1520 b areoriented at approximately −30° with respect to the x-axis.

ADDITIONAL CONSIDERATIONS

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,”“include,” “including,” “have” and “having” and the like are to beconstrued in an inclusive sense, as opposed to an exclusive orexhaustive sense; that is to say, in the sense of “including, but notlimited to.” The word “coupled”, as generally used herein, refers to twoor more elements that may be either directly connected, or connected byway of one or more intermediate elements. Likewise, the word“connected”, as generally used herein, refers to two or more elementsthat may be either directly connected, or connected by way of one ormore intermediate elements. Depending on the context, “coupled” or“connected” may refer to an optical coupling or optical connection suchthat light is coupled or connected from one optical element to anotheroptical element. Additionally, the words “herein,” “above,” “below,”“infra,” “supra,” and words of similar import, when used in thisapplication, shall refer to this application as a whole and not to anyparticular portions of this application. Where the context permits,words in the above Detailed Description using the singular or pluralnumber may also include the plural or singular number, respectively. Theword “or” in reference to a list of two or more items is an inclusive(rather than an exclusive) “or”, and “or” covers all of the followinginterpretations of the word: any of the items in the list, all of theitems in the list, and any combination of one or more of the items inthe list, and does not exclude other items being added to the list. Inaddition, the articles “a,” “an,” and “the” as used in this applicationand the appended claims are to be construed to mean “one or more” or “atleast one” unless specified otherwise.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: A, B, or C” is intended to cover: A, B, C,A and B, A and C, B and C, and A, B, and C. Conjunctive language such asthe phrase “at least one of X, Y and Z,” unless specifically statedotherwise, is otherwise understood with the context as used in generalto convey that an item, term, etc. may be at least one of X, Y or Z.Thus, such conjunctive language is not generally intended to imply thatcertain embodiments require at least one of X, at least one of Y and atleast one of Z to each be present.

Moreover, conditional language used herein, such as, among others,“can,” “could,” “might,” “may,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements, and/or states arein any way required for one or more embodiments or whether thesefeatures, elements, and/or states are included or are to be performed inany particular embodiment.

Unless stated or illustrated otherwise, or evident to a person ofordinary skill in the art from context, words like “about,”“approximately,” and “generally” used in connection with a stated valueor other descriptor can be understood to indicate a range of ±20% aroundthe stated value.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosure. Features of any one of the embodiments can becombined and/or substituted with features of any other one of theembodiments. Certain advantages of various embodiments have beendescribed herein. But not all embodiments necessarily achieve each ofthese advantages.

Embodiments have been described in connection with the accompanyingdrawings. However, the figures are not drawn to scale. Distances,angles, etc. are merely illustrative and do not necessarily bear anexact relationship to actual dimensions and layout of the devicesillustrated.

The foregoing embodiments have been described at a level of detail toallow one of ordinary skill in the art to make and use the devices,systems, methods, etc. described herein. A wide variety of variation ispossible. Components, elements, and/or steps may be altered, added,removed, or rearranged. While certain embodiments have been explicitlydescribed, other embodiments will become apparent to those of ordinaryskill in the art based on this disclosure.

What is claimed is:
 1. An eyepiece for a virtual reality, augmentedreality, or mixed reality system, the eyepiece comprising: first andsecond waveguide substrates that are at least partially transparent; aninput coupler grating formed on or in each of the first and secondwaveguide substrates and configured to couple at least one respectiveinput light beam that is externally incident on the input couplergrating into at least a respective first guided light beam thatpropagates inside the respective first and second waveguide substrates;a first orthogonal pupil expander (OPE) grating formed on or in each ofthe first and second waveguide substrates and configured to divide therespective first guided light beam from the respective input couplergrating into a respective plurality of parallel, spaced-apart lightbeams; and an exit pupil expander (EPE) grating formed on or in each ofthe first and second waveguide substrates and configured to re-directthe respective light beams from the respective first OPE grating suchthat they exit the respective first and second waveguide substrates, theEPE grating comprising a plurality of curved lines whose curvaturedetermines an amount of optical power of the EPE grating, wherein thefirst and second waveguide substrates are configured to respectivelyoutput a plurality of output beams such that they correspond todifferent respective first and second depth planes, the first and seconddepth planes being determined by the respective optical powers of theEPE grating of the first waveguide substrate and the EPE grating of thesecond waveguide substrate, the EPE grating of the second waveguidesubstrate comprising an amount of optical power that is different thanthe optical power of the EPE grating of the first waveguide substrate.2. The eyepiece of claim 1, wherein the first waveguide substrate isless than 325 microns thick.
 3. The eyepiece of claim 1, wherein thefirst waveguide substrate comprises glass, plastic, or polycarbonate. 4.The eyepiece of claim 1, wherein the first waveguide substrate isconfigured to project a color component of image data.
 5. The eyepieceof claim 1, further comprising a projector to direct light toward theinput coupler grating of the first waveguide substrate and toward theinput coupler grating of the second waveguide substrate.
 6. The eyepieceof claim 1, wherein the input coupler grating is configured to divideand re-direct the at least one input light beam that is externallyincident on the input coupler grating into first and second guided lightbeams that propagate inside the first waveguide substrate, the firsteyepiece waveguide further comprising: a second OPE grating formed on orin the substrate and configured to divide the second guided light beamfrom the input coupler grating into a plurality of parallel,spaced-apart light beams, wherein the EPE grating is configured tore-direct the light beams from the first and second OPE gratings suchthat they exit the first waveguide substrate, and wherein the inputcoupler grating is positioned between the first OPE grating and thesecond OPE grating and is configured to direct the first guided lightbeam toward the first OPE grating and to direct the second guided lightbeam toward the second OPE grating.
 7. The eyepiece of claim 6, whereinthe input coupler grating is configured to separate the input light beaminto a +1 diffractive order directed toward the first OPE grating and a−1 diffractive order directed toward the second OPE grating.
 8. Theeyepiece of claim 6, wherein the first and second OPE gratings areseparated by approximately 180° and the EPE grating is located at about90° to both OPE gratings.
 9. The eyepiece of claim 6, wherein the firstand second OPE gratings are slanted toward the EPE grating.
 10. Theeyepiece of claim 9, wherein the first and second OPE gratings areseparated by approximately 120° and the EPE grating is located at about60° to both OPE gratings.
 11. The eyepiece of claim 6, wherein the inputcoupler grating comprises diffractive optical features to divide andredirect the input light beam toward the first and second OPE gratings.12. The eyepiece of claim 11, wherein the diffractive optical featuresof the input coupler grating comprise a plurality of lines forming atleast one diffraction grating.
 13. The eyepiece of claim 11, wherein thediffractive optical features of the input coupler grating comprise aplurality of features laid out on in a lattice pattern.
 14. The eyepieceof claim 13, wherein the lattice pattern comprises a hexagonal lattice.15. The eyepiece of claim 11, wherein the diffractive optical featuresof the input coupler grating comprise a crossed grating.
 16. Theeyepiece of claim 11, wherein the diffractive optical features of theinput coupler grating are configured to direct light toward the firstand second OPE gratings, and toward the EPE grating without firstpassing through either of the OPE gratings.
 17. The eyepiece of claim 6,wherein the first and second OPE gratings comprise diffractive opticalfeatures to divide each of the first and second guided light beams intothe plurality of parallel, spaced-apart light beams.
 18. The eyepiece ofclaim 17, wherein the diffractive optical features of the first andsecond OPE gratings comprise a plurality of lines forming diffractiongratings.
 19. The eyepiece of claim 18, wherein the diffraction gratingsof the first and second OPE gratings are angled so as to direct theplurality of spaced-apart light beams toward the EPE grating.
 20. Theeyepiece of claim 6, wherein the first waveguide substrate furthercomprises: a first spreader grating that receives the light beams fromthe first OPE grating and spreads their distribution so as to reach alarger portion of the EPE grating; and a second spreader grating thatreceives the light beams from the second OPE grating and spreads theirdistribution so as to reach a larger portion of the EPE grating.
 21. Theeyepiece of claim 20, wherein the first spreader grating and the secondspreader grating are both configured to spread the distribution of thelight beams toward the center of the EPE grating.
 22. The eyepiece ofclaim 20, wherein the first and second spreader gratings comprisediffractive optical features.
 23. The eyepiece of claim 22, wherein thediffractive optical features of each of the first and second spreadergratings comprise a plurality of lines that form diffraction gratings.24. The eyepiece of claim 23, wherein the diffraction grating of thefirst spreader grating is oriented at approximately 90° to a diffractiongrating of the first OPE grating, and wherein the diffraction grating ofthe second spreader grating is oriented at approximately 90° to adiffraction grating of the second OPE grating.